The overall objective of this research program is to understand the molecular events which take place during endocytosis of immune complexes or target particles. Immune complexes are involved in many acute and chronic diseases. Macrophages take part in both the clearance of immune complexes from the circulation and tissue injury following immune complex deposition. We intend to identify in situ the cell surface components which are associated with immune complex clearance. A localized radioiodination technique will be employed to label surface proteins during immune complex recognition and handling. In addition, we intend to study bulk membrane flow and specific membrane component flow during phagocytosis. Bulk membrane flow and recycling will be examined with a non-perturbing carbohydrate-labeling protocol. Specific membrane flow and recycling will be studied using Fab' fragments of antibodies against cell surface glycoproteins coupled via a disulfide bridge to a heterobifunctional photo-activated affinity label. These studies will provide important and complimentary information regarding the mechanism of phagocytosis, a critical host defense mechanism.